Description:

Automobile emissions control has become a very important cornerstone of the
Clean Air Act of 1990. Automobile emissions standards and automobile emissions
testing continue to have a significant positive impact on metropolitan air
quality. In order to continue improving air quality, emission standards and
testing have become more stringent. The Clean Air Act of 1990 required the EPA
to develop standards for new automobiles and certification testing of older
automobiles. Most states currently employ annual (or bi-annual) automobile
emissions testing, and a significant fraction have proceeded to enhanced
emissions testing. The EPA requires on-road monitoring of operating vehicles to
be an integral part of an enhanced emissions testing program. The ultimate goal
of on-road monitoring is to identify automobiles that emit excess pollution so
that corrective action may be taken. While privacy and legal concerns may
constrain the use of remote sensing to achieve these goals, remote sensing of
automobile emissions is currently being used by a number of states. Remote
sensing is expected to improve the ability of states to monitor automobile
emissions and result in significant cost reductions associated with "clean
screening" programs, where low emitters are exempted from annual enhanced
emissions inspections. The development of accurate remote sensing systems for
automobile pollution monitoring is expected to be an important factor for
improving the air quality of major metropolitan areas.

While there are a number of techniques available for remote sensing of
automobile emissions, many of these techniques have significant performance
limitations. Remote sensing systems based upon Light Detection and Ranging
(LIDAR) are very promising for standoff detection of various pollution gasses.
Most LIDAR systems have been developed for long range (> 1 km) monitoring to
measure atmospheric variations of pollution. While the ability to remotely probe
over great distances is important, these systems are usually expensive and
cumbersome. By adapting these LIDAR techniques to short range applications (~10
m), significant cost and size savings will be realized, as well as improved
detection sensitivity. The inherent advantage of the proposed Raman LIDAR system
is that the transmitter and receiver can be co-located, eliminating the need for
remotely locating the receiver or retro-reflector. This greatly simplifies the
placement and set up of the remote emissions monitor. In addition, Raman LIDAR
is self-calibrating to atmospheric oxygen and nitrogen, eliminating requirements
for periodic calibration with test gasses. Finally, the system can determine the
concentration of emission gasses as a function of range, enabling the system to
localize the source of the emissions across a multi-lane highway. In Phase I of
this SBIR program, we have demonstrated feasibility and completed the
preliminary design for a functional prototype automobile emissions monitoring UV
Raman LIDAR that will be produced in Phase II.

To achieve sufficient sensitivity for automobile pollution monitoring, the UV
Raman LIDAR system must incorporate a high efficiency optical collection system
and spectral analysis system. Radiation Monitoring Devices, Inc. (RMD) has
completed the preliminary design of this optical receiver system, which has been
optimized by an optical design consultant using state-of-the-art optical design
software tools. RMD has also demonstrated a high efficiency linear avalanche
photodiode detector (APD) array, which will be incorporated into the system to
provide high efficiency detection of the spectrally resolved Raman return
signal. The linear APD array geometry will be matched to the spectrometer output
to optimize the system sensitivity and wavelength resolution. In Phase I, RMD
also performed laboratory UV Raman LIDAR experiments to demonstrate that UV
Raman LIDAR is very promising for remote sensing of automobile emissions.

This report summarizes the progress RMD has made on the following tasks
delineated for this Phase I SBIR: 1) System analysis to determine the
performance characteristics required for the short Range UV Raman LIDAR; 2)
Laboratory demonstration of UV Raman LIDAR confirming the sensitivity estimates
in the system analysis; and 3) Preliminary design of the optical system for the
Phase II prototype. RMD has successfully completed all of the Phase I tasks and
is confident that prototype development during Phase II will lead to a
commercial remote emissions monitor using UV Raman LIDAR.

Summary/Accomplishments (Outputs/Outcomes):

The system analysis indicates that UV Raman LIDAR is an excellent candidate
for remote sensing of automobile emissions. The variables that were analyzed
include excitation wavelength and energy, Raman scattering cross section,
receiver aperture, and range to automobile. The analysis indicates that, for
reasonable design assumptions, the system will be capable of achieving a
detection limit of 1-100 ppm for most gasses of interest. Some gasses, such as
SO2 will achieve a detection limit better than 1 ppb due to an enhanced Raman
cross section. These detection limits are sufficient for on-road emissions
testing to detect low emitters for clean screening applications as well as early
detection of gross emitters to expedite repair of failed emissions systems.

The laboratory experiments included the design and construction of a custom
Raman LIDAR test chamber. Various test gasses were introduced into the Raman
LIDAR test chamber and the Raman backscatter returns were analyzed as a function
of wavelength and gas pressure. The results indicate an excellent ability to
identify and quantify the test species. By analyzing the sensitivity of these
Phase I laboratory experiments, we estimate that the Compact UV Raman LIDAR
system will be capable of achieving better than 120 parts per million (PPM)
sensitivity for NO, 40 ppm for N2 and CO, and 10 ppm for NO2 and
hydrocarbons.

In addition to the laboratory experiments, we developed the preliminary
optical design for the Phase II prototype optical receiver. This design takes
advantage of RMD's unique large area linear APD detector arrays to maximize the
detection efficiency for the Raman backscatter return. The Raman return is
spectrally resolved with ~1 nm resolution, which is sufficient to uniquely
identify the typical pollution species from an automobile exhaust. This
preliminary design will be implement in the Phase II prototype to demonstrate
the full capabilities of the UV Raman LIDAR for automobile emissions
monitoring.

Finally, RMD completed the Phase I commercialization analysis. Foresight
Science and Technology, Inc. (FST) found that RMD's unique approach to
automobile emissions monitoring is an attractive solution and could be expected
to perform well in the commercial marketplace. In addition to FST, RMD is
working with the Massachusetts STrategic Envirotechnology Partnership (STEP) to
facilitate commercialization of the automobile emissions LIDAR. RMD participated
in a Commercialization Partnering Assistance roundtable organized by STEP to
assist in the commercialization of the UV Raman LIDAR for automobile emissions
monitoring. The participants in the roundtable were very excited about the
potential of UV Raman LIDAR for automobile emissions monitoring. We believe that
the development of the Compact UV Raman LIDAR prototype in Phase II will result
in the successful commercialization of the automobile emissions monitor.

Conclusions:

RMD has successfully completed all of the Phase I tasks and demonstrated the capabilities of Raman LIDAR for remote sensing of automobile emissions monitoring. The system design developed during Phase I will lead to the successful completion and field testing of the prototype automobile emissions UV Raman LIDAR system in Phase II. The UV Raman LIDAR system is expected to enable a variety of commercial environmental monitoring products, including automobile emissions monitoring, light and heavy duty truck emissions monitoring, aircraft emissions monitoring, warning systems for toxic chemical spills, and fence line monitoring. The advantages of UV Raman LIDAR for these applications include co-location of the transmitter and detector, continuous self-calibration, and range resolving capability that will enable operation across multi-lane highways. In addition, it is envisioned that the system can be readily upgraded for particulate monitoring applications by incorporating additional detector elements to monitor the aerosol LIDAR return.

Progress and Final Reports:

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.